Fabrication Of Patterned And Free-Standing Layer-by-Layer Assembled Multilayer Films

Layer-by-Layer(LbL) assembly technique has attracted more and more attention of scientists in recent years because of its simplicity in film preparation and flexibility in film structure control. LbL assembly technique has been widely applied in materials science. Although many methods on fabricating patterned and free-standing multilayer films have been established, universal approaches that are particularly suitable for preparing patterns with reduced feature sizes and facile methods without the use of sacrificial layer or complete removal of substrate are still highly desirable. In this dissertation, it is demonstrated that patterned polymeric multilayer films of poly(acrylic acid) (PAA)/poly(allylamine hydrochloride) (PAH), PAH/poly-(sodium 4-styrenesulfonate) (PSS) can be fabricated by room-temperature nanoimprinting lithography (RT-NIL). Meanwhile, a facile way to prepare poly(acrylic acid) (PAA)/poly(allylamine hydrochloride) (PAH) free-standing films by exfoliating PAA/PAH multilayer films from substrates in aqueous solution containing Cu2+ ions was also developed.In charpter 1, we summarized the process of LbL assembly technique for fabricating LbL assembled multilayer films. We focused mainly on the electrostatic LbL assembly technique, and describes the details for the treatment of substrates, the driving force for the preparation of polyelectrolyte multilayer films, absorption kinetics of polyelectrolytes, the parameters which can control over the thickness of multilayer films, the structure of polyelectrolyte multilayer films and so on. In charpter 2, we prepared patterned multilayer films by room-temperature nano-imprint lithography (RT-NIL). The process for patterning polyelectrolyte multilayer films by RT-NIL was characterized systematically AFM and SEM. Nanoimprint lithography (NIL) is a newly developed patterning method that uses a hard mold to imprint micro and nanostructures onto a substrate coated with polymeric material. The recently developed room-temperature nano-imprint lithography (RT-NIL) indicates that the imprint of some polymers at room temperature is possible, but the number is very limited. RT-NIL enables multi-imprinting and facilitates the nanofabrication process. This work is meaningful in at least two respects: i) it will open new routes to pattern layered polymeric multilayers for further applications; ii) the layered polymeric films are potentially usable as RT-NIL resists for nanofabrication.In charpter 3, we reported a facile way to prepare poly(acrylic acid) (PAA)/poly(allylamine hydrochloride) (PAH) free-standing films by exfoliating PAA/PAH multilayer films from substrates in aqueous solution containing H+ and Cu2+ ions. Free-standing films are expected to broaden further the application of LbL assembled multilayer films, especially as separation membrances, sensors, catalytic film, micromechanical devices, or even artificial organs. Although there exist several method to prepare free-standing LbL assembled multilayer films, facile methods without the use of sacrificial layer or complete removal of substrate are still highly desirable. In this communication, we reported a facile way to prepare poly(acrylic acid) (PAA)/poly(allylamine hydrochloride) (PAH) free-standing films by exfoliating PAA/PAH multilayer films from substrates in aqueous solution containing H+ and Cu2+ ions. This work will open a new route to fabricate LbL assembled free-standing films by using ion-triggered exfoliation method.